Is it really necessary to use premium gas in a 2004 Eclipse GTS?


Asked by May 16, 2007 at 10:34 AM about the 2004 Mitsubishi Eclipse GTS

Question type: Maintenance & Repair

I have recently purchased the GTS and since the gas prices have gone through the roof, I was wondering if it was necessary to use Premium? What octane should I not go below?

12 Answers

I think its only recommended that you use premium, not required.

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you will get better gas milage and your car will run smoother if you use it

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If the GTS's V6 is designed for premium (which if i remember correctly, it is), you should stick with that. Basically there's a certain quality level in premium fuel, and if you drop down, you'll start wearing the fuel system out. also, the engine's made to run on premium so you wont get as good of gas mileage and power. Stepping up in octane is always good, but avoid stepping down if possible.

4 people found this helpful.

They recomend running premium because of high compression. It keeps the motor from predetonation or "knocking" or "Pinging". Too much knocking will end up wearing the motor out. As far as gas miliage.. I have never noticed or heard of a significant difference between regular or premium. So its good to go higher octane. 10 gallons at $3.30 for regular = $33 10 gallons at $3.50 for premium = $35 $2 every fill up isnt bad for a relyable motor.

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Generally speaking the octane ratings are higher than advertised. That is a 'minimum' rating after all. However, that being said the comments on pre-detonation wearing out the engine or damaging the valve train are true. Another trouble may be incomplete combustion, which can cause run-on after you turn off the engine (less common but not unheard of in FI engine). Also wears out the engine because the revs drop way down and cylinders fire unbalanced causeing uneven strain on the rotating assembly. My opinion would be not to drop below 89 octane in your car requests 91. Granted I would recommend the 91 just because they generally have more ditergants in them and keep your valves from sticking in the long run.

5 people found this helpful.

i have an 03 eclipse GT and i put plus in my car. it runs great! but prices suck. lol


remember one thing.. when you use a lower than recommended octane fuel in a high compression engine, several things happen. 1 the timing will retard because the knock sensor senses engine ping. Thus.. 2 , lower power, 3, rough idle, 4, mpg will decrease. Use lower octane long enough and you risk burning holes in the pistons and making a mess of the valves

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I am so upset. I have a Mitshibushi 2003 Eclipse GTS V6. My husband said you don't necessarily need premium but can use unleaded. Now the darn thing is running rough. I have a check engine light on and took it into a mechanic and he said I have a vacuum leak and its runs rough and sounds terrible when starting up but not in a minute, it stops and runs smooth. Mechanic said it would cost around $1,600 to fix. I love this car! Ugh, I am never going to listen to him again, When I had premium in there I had no problems....................

4 people found this helpful.

We have Mitsubishi Endeavor 2005, since 2006. It requires premium gasoline which I must use it or damage to engine could be severe. Next time before buying another vehicle I will be looking in owner manuals first. It hurts a lot at gas pumps. I wouldn't buy next vehicle which required premium gasoline, no matter what. I tried using lower grade but it ended using more gas.

Its good to have high octane only if your car needs it,most cars are now engineered to run on basic fuels.The issue is that using cheaper fuels will contain moisture and less detergents that help clean the engine.Higher octane fuel contains more detergents and increases the ignition timing which might reduce knocking on certain cars.It might also slightly give you better mileage but it will not give you better mileage that what your car originally gave you when it was new. It will MAINTAIN that mileage.As long as you don't go lower than what the manufacturer recommended in octane levels you will be fine.Good luck


I have an 02 gt that recommends premium fuel and I have used both and the only difference that I have noticed is that the high end performance is slightly reduced running 87 octane .

1 people found this helpful.

higher octane = longer explosion burn time which pushes on the piston longer and increases power and mileage. Shorter explosion time damages parts over time. I can get 35+ mpg on the highway easily with premium.

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